Galvanometer mirrors have been widely used as light deflectors in various optical scanning devices, e.g. optical imaging devices, light projecting devices, non-impact optical printers in the art, the galvanometer mirror is angularly moved in reciprocating strokes when a sawtooth sinusoidal or other repetitive current is supplied to the mirror drive.
An excellent example of the optical scanning for imaging is found in U.S. Pat. No. 4,627,734, Dec. 9, 1986 (Rioux). In his patent, Rioux describes an optical three dimensional imaging system using a laser synchronous scanner which scans an object by a beam of light and receives synchronously scattered light from the object. By processing the received scattered light signal, a three dimensional image is reconstructed.
In U.S. Pat. No. 4,648,685, Mar. 10, 1987 Fukai et al, a specifically designed sawtooth voltage waveform is employed to scan a flat surface at variable speeds for different directions.
For data gathering and image reproduction by optical scanning, it is necessary to synchronize the scanner to external drive electronics and to generate a pixel clock to strobe data either in or out of user hardware. Although low cost microprocessors and high speed complex logic elements have made this easier and more affordable, such synchronization with accuracy and precision is still complex.
Many patents describe variety of techniques for resolving various problems encountered in galvanometric scanners.
U.S. Pat. No. 4,127,781, Nov. 28, 1978 (Sato), for example, teaches a system for determining accurately the position of the scanning mirror. It uses a rectangular uniformily distributed light which is reflected from the back surface of the mirror across a plurality of parallel photovoltaic diode structure bars.
U.S. Pat. No. 4,044,248, Aug. 23, 1977 (Glassnian), on the other hand, describes a method and an apparatus for linearizing a mirror galvanometer. The patent uses a transmission grating in the path of the beam. The grating modulates the scanned beam in accordannce with the velocity of scan of the light beam. A control signal is produced by processing the output from a photocell monitoring the scanned beam and is combined with a reference driving signal to deflect the mirror in linear fashion.